1. Field of the Invention
The present invention relates to a TiAl alloy which comprises titanium and aluminum and also niobium and molybdenum and/or manganese and is referred to in technical circles as TNM alloy.
2. Discussion of Background Information
TiAl alloys based on the intermetallic phase γ-TiAl are predestined for use in flow machines such as stationary gas turbines and aircraft engines because of their low specific weight and the high strength due to the ordered intermetallic phase. Thus, for example, US 2011/0189026 A1, the entire disclosure of which is incorporated by reference herein, describes a TiAl-based alloy for the production of gas turbine components. The alloy described there is a TNM alloy containing from 42 to 45 at. % of aluminum, from 3 to 8 at. % of niobium and from 0.2 to 3 at. % of molybdenum and/or manganese. In addition, from 0.1 to 1 at. % of boron and/or carbon and/or silicon can be present. The balance of the alloy is formed by titanium. Alloys of this type, which comprise, in particular, 43.5 at. % of aluminum, 4 at. % of niobium, 1 at. % of molybdenum and 0.1% of boron with titanium as balance, are suitable for use at operating temperatures of from 750° C. to 780° C.
The microstructure of such TNM alloys is built up in a complex manner of a plurality of phases and comprises γ-TiAl, α2-Ti3Al and βo/B2-titanium.
A further alloy having a microstructure made up of γ-TiAl, α2-Ti3Al and β-phase is described in US 2011/0277891, the entire disclosure of which is incorporated by reference herein. This alloy comprises from 42 to 44.5 at. % of aluminum, from 3.5 to 4.5 at. % of niobium, from 0.5 to 1.5% of molybdenum, up to 2.2 at. % of manganese, from 0.05 to 0.2 at. % of boron, from 0.001 to 0.01 at. % of silicon, from 0.001 to 1.0 at. % of carbon, from 0.001 to 0.1 at. % of oxygen, from 0.0001 to about 0.002 at. % of nitrogen with titanium and impurities as balance.
However, the usability of the TNM alloys described is restricted to temperatures below 800° C. since an unsatisfactory creep resistance is observed during prolonged use at higher temperatures and this results in an unsatisfactory life for use in flow machines such as stationary gas turbines or aircraft engines.
It would therefore be advantageous to have available a TiAl alloy which has relatively high use temperatures in the range above 800° C. and in particular an improved creep resistance. Furthermore, it would be advantageous to have available components made of the corresponding alloy, in particular for flow machines, particularly aircraft engines.